Police have charged an 18-year-old with manslaughter over the death of a South Auckland teenager shot with an airgun.

Shaun Townsley, 18, of Takanini, allegedly strayed into the line of fire while a group of friends were drinking and using airguns to take pot shots at cans in their backyard on January 12.

He died at Middlemore Hospital the next morning. An autopsy showed Townsley was hit in the heart.

Counties Manukau police said today that an 18-year-old from Manurewa had been charged with manslaughter. He will appear in the Manukau District Court tomorrow.

In the wake of the death, police had to reconstruct what happened and consult with lawyers before laying charges.

Detective Inspector Dave Lynch warned at the time that airguns were powerful weapons that had the potential to kill or seriously injure.

"This tragedy should serve as a painful reminder that these weapons are not toys and need to be used in a controlled environment by responsible people with appropriate target awareness and knowledge of their power."

The group were using two types of guns - a Crosman 357 Magnum .177 calibre air pistol and a Crosman Nitro Venom .177 calibre break-barrel air rifle, which was believed to be the weapon used for the fatal shot.

Crosman markets the rifle, which has a spring piston firing mechanism, as a hunting weapon capable of firing at up to 305m per second.

Anyone 18 years or older can own and use an airgun without a firearms licence.

In 2010 the law surrounding certain airguns changed after they were used in the murders of police officer Don Wilkinson and Auckland man Keith Kahi.

Owners now require a firearms licence to own pre-charged pneumatic-powered guns.